Fixes issue #1712: New-AzureAffinityGroup help text about affinity groups

This is a PS doc fix that @cromwellryan authored a few months ago. I'd like to submit this for consideration in this release. That fix was in https://github.com/WindowsAzure/azure-sdk-tools/pull/1714

The text from that fix:

from ```help New-AzureAffinityGroup```:

> -Location <String>
>         Required **if AffinityGroup is not specified**. The Location parameter specifies the geographical location of the data center where the affinity group will be created.

Location is a) not optional and you can't nest affinity groups.